Information processing systems in which a plurality of nodes (information processing apparatus, such as computers, or storage apparatus, for example) are connected via a plurality of relay apparatus are used. These relay apparatus relay communication between nodes and form a network.
Redundant communication paths may be set in networks. Even if one of a plurality of communication paths set cannot be used, communication can be continued by the use of another communication path. As a result, the reliability of a network can be improved. For example, verifying the reliability of a network by tracing a connection relationship in the network from an access source apparatus to an access destination apparatus and determining whether or not there is a redundant route between them is proposed.
Furthermore, if communication is performed by selecting one of a plurality of links the cost of which is low, the following method for saving power is proposed. Communication is centralized on one link by making the cost of a high usage link low. When the usage of the other links becomes zero, power is disconnected from the other links. After that, when the usage of the link on which communication is centralized rises further to a determined value, power is applied to the other links, which are in a power off state, to restore redundancy.    Japanese Laid-open Patent Publication No. 2006-174157    Japanese Laid-open Patent Publication No. 2010-187166
By the way, there are cases where the level of the redundancy of communication paths between relay apparatus is higher than that of the redundancy of communication paths (number of communication paths) ensured on a node side.
For example, interface units for making a connection to a network the number of which corresponds to the level of redundancy ensured are included on the node side. On the other hand, a new node may be connected to a relay apparatus after its installation in order to enhance throughput or add a function. Accordingly, in order to avoid a subsequent change in connection between the relay apparatus, a connection structure which can accommodate a future increase in traffic or the like may be prepared in advance. However, the level of redundancy ensured on the node side may not match the level of the redundancy of communication paths between the relay apparatus and the latter may be higher than the former.
In this case, how to efficiently reduce the number of excess communication paths between the relay apparatus matters. For example, it takes many man-hours for a system administrator to perform the work of checking whether or not there are excess communication paths for each node. This method is inefficient. In particular, as the scale of a network grows, this work becomes more difficult.